High strength copper alloy for electronic parts and electronic parts

ABSTRACT

A copper base alloy for electronic parts containing 2.0 to 4.0 mass % of Ti and 0.05 to 0.50 mass % of one or more of Fe, Co, Ni, Si, Cr, V, Nb, Zr, B and P, wherein the content of other impurity elements is 0.010 mass % or less in total, and the content of each of C and O is 0.010 mass % or less. This copper base alloy can be used without heat treatment after its press working into a part of a connector or the like; or can be also used in a state in which the alloy is subjected to a specific heat treatment so as to be improved in spring characteristics after its press working.

TECHNICAL FIELD

The present invention relates to a copper alloy used in such products as connectors (contacts). Specifically, the present invention provides a copper alloy having excellent spring property and electronic components using said copper alloy.

BACKGROUND OF THE INVENTION

Copper alloys containing titanium (herein referred to as “titanium-copper alloys”) have the next excellent strength to beryllium-copper alloys in the copper alloy family, while the stress relaxation property of titanium-copper alloys exceeds that of beryllium-copper alloys. Titanium-copper alloys therefore are used in electronic components such as connectors, and the demand of use of titanium-copper alloys is now steadily increasing and higher strengths and higher bendability are required.

To cope with the situation, new technique has been indicated in order to achieve higher strength of titanium-copper alloys by the addition of Cr, Zr, Ni and Fe (e.g. Japanese Patent Application Publication No. H6-248375). Also, technique directing to refinement of crystal grains has been disclosed (e.g. Japanese Patent Application Publication No. 2001-303158). Further, technique of addition of Zn, Cr, Zr, Fe, Ni, Sn, In, P and Si into titanium-copper alloys has also been discussed (e.g. Japanese Patent Application Publication No. 2002-356726).

[Prior art 1] Japanese Patent Application Publication No. H6-248375

[Prior art 2] Japanese Patent Application Publication No. 2001-303158

[Prior art 3] Japanese Patent Application Publication No. 2002-356726

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

Titanium-copper alloy is an age hardening copper alloy that forms a supersaturated solid-solution by solution treatment and a modulated structure of a metastable phase is developed by aging treatment. During a certain period of developmental stage, remarkable hardening of the copper alloy occurs. Due to the behavior of the alloy, the alloy is pressed to the form of parts such as electronic components after solution treatment, cold rolling, and aging treatment.

After aging treatment, parts obtained by press forming with severe bending may have residual strain in bending zones that may cause problems during use. For this reason, in the case of severe bending of age hardening copper alloys, it is popular to perform solution treatment, cold rolling, pressing without aging treatment, and then aging treatment. However, titanium-copper alloys before aging treatment have poor ductility, and therefore cracks easily occur in severe bending zones of pressed zones. Even if press forming can be performed without problems such as cracks before aging treatment, a dimensional change occurs after aging treatment due to development of a modulated structure causing significant shape deformation. In addition to the above, even if such cracking and deformation problems are solved, the spring property after press forming is inferior to those of the materials of C1720 (beryllium-copper alloy) obtained after aging.

The present invention was accomplished in view of the problems recited above and provides a copper alloy that can be used as parts such as connectors without any process after press forming. When better spring property is necessary, additional heat treatment at low temperatures after pressing provides excellent spring property substantially equivalent to that of C1720 (beryllium-copper alloy).

Means for Solving the Problem

The present inventors researched the effects of O and C on the added elements such as Fe and Cr in titanium-copper alloy-type copper alloys, and found that minimizing the contents of O and C improves strength of the alloy and enables the addition of Fe, Cr and the like to effect on the copper alloy, resulting in the copper alloy having excellent strength, conductivity and bendability even when the aging treatment temperature is reduced. Further to the above, it was discovered that suitable heat treatment after pressing reinforces strength of the bending zone and also improves spring property.

In other words, the present invention includes the following.

(1) A copper alloy for electronic components including a copper-based alloy having 2.0-4.0 mass % of Ti, 0.05-0.50 mass % in total of one or more elements selected from the group consisting of Fe, Co, Ni, Si, Cr, V, Nb, Zr, B and P, and the balance being Cu and other impurity elements,

-   -   wherein the total amount of other impurity elements is 0.050         mass % or less; and the contents of each C and O are 0.010 mass         % or less.         (2) A copper alloy for electronic components comprising 2.0-4.0         mass % of Ti, 0.05-0.50 mass % of Fe, and the balance being Cu         and other impurity elements,     -   wherein the total amount of other impurity elements is 0.050         mass % or less; and the contents of each C and O are 0.010 mass         % or less.         (3) The electronic component prepared from the copper alloy of         the above (1) or (2) wherein the hardness is adjusted by heat         treatment at a temperature of 400° C. or less after pressing of         the copper alloy into a predetermined shape.

The copper alloy of the present invention has excellent bendability, and importantly, not only cracks in the periphery of the bending zone upon bending are prevented, but also the thickness of the bending zone is uniformly even. These properties are caused by relatively high resistance against compressive deformation in the thickness direction as compared to the resistance against the deformation in other directions. As a result, necking in the thickness direction hardly occurs during bending in the copper alloy of the present invention. Therefore, the copper alloy of the present invention are preferable for spring materials subjected to pressing. If, for example, the thickness of the bending zone is not uniform and a necking zone appears in the thickness direction, stress is concentrated therein and spring property is deteriorated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a connection of connectors.

FIG. 2 illustrates the shape of a test piece used in a spring property test of Evaluation 1.

FIG. 3 illustrates the spring property test of Evaluation 1.

FIG. 4 is an example of a load-deflection curve obtained by a spring property test of Evaluation 1.

FIG. 5 is an example of a connection of connectors.

FIG. 6 illustrates the shape of a test piece used in a spring property test of Evaluation 2.

FIG. 7 illustrates the spring property test of Evaluation 2.

EFFECT OF THE INVENTION

As described above, the present invention is able to achieve excellent bendability, higher strength and better punchability at high level simultaneously by controlling the amount of impurities and trace gas elements below predetermined values in titanium-copper alloys having additives of group III elements.

In addition, if adequate heat treatment is performed after press forming, the alloy of the present invention exhibits remarkable improvements of spring property not achieved in the titanium-copper alloys without additives of group III elements.

Therefore, the present invention is advantageous for producing copper alloys preferable for electronic components such as connectors.

THE BEST MODE FOR CARRYING OUT THE INVENTION

A phenomenon in which yield stress of iron and steel is improved by heat treatment at a low temperature after cold working is commonly known as strain aging. A similar phenomenon observed in solid-solution hardening type copper alloys such as brass is known as low-temperature anneal hardening, and a phenomenon observed in titanium-copper alloys wherein a modulated structure was developed is known as Mechanico-Thermal Hardening (MTH) processing. However, in all of the phenomena reported for MTH processing of titanium-copper alloys, the cold working ratio is relatively high, and the heating time of the subsequent heat treatment is relatively short.

Specifically, many reports discuss experiments with working ratios of 50%-90% and heating times of 1 to 10 minutes. Accordingly, it can hardly be said that the phenomena recited above are practically used to improve spring property of leaf springs for commercial use for the following reasons. In forming process of a leaf spring by using a pressing machine, even at the site applied with the maximum working ratio is not processed with high working ratios with which low-temperature anneal hardening are observed. Further, heat treatment after press forming is performed not for single product at one time, but for a large number of products in a batch oven at one time. However, because a batch oven requires much time for steady state of the temperature in the oven from starting of the heating, stable operation is impossible with short heating times. In the present invention, however, sufficient hardening is achieved by means of the relatively low working ratio of 10% or less and subsequent heat treatment with a relatively long time of 1 to 5 hours at 340-360° C. Therefore the present invention is commercially feasible from a viewpoint of stability in manufacturing. The above phenomena are not observed in usual titanium-copper alloys, but only in the titanium-copper alloy manufactured by adding specific group III elements in proper amounts to the alloy, limiting the contents of the impurity elements therein, and carrying out the adequate processes.

Meanwhile, when the product of the present invention are heated to around 300° C. after cold working, ductility is recovered as well as softening occurs. In other words, when the alloy of the invention is heated at a low temperature below 400° C., hardening regardless of the degree never occurs, but heating at too low temperature results in a softening phenomenon. A conversion from softening to hardening occurs at about 320-330° C. depending on somewhat the cold working ratio and the type and amount of the added elements. A remarkable phenomenon in this conversion is observed in which strength drastically increases with only slight temperature differences. No such phenomenon has been reported for generally-known low-temperature anneal hardening or MTH. This phenomenon is discovered for the first time in the present invention.

(1) Composition of Copper Alloys (a) Ti

In the present invention, Ti content is specified as 2-4 mass %. Strength is insufficient when Ti is less than 2 mass %, and bendability deteriorates when Ti is more than 4 mass % due to coarse precipitates which tend to appear. The most preferable content of Ti is 2.5-3.5 mass %.

(b) Group III Elements

The present invention specifies the addition of group III elements. The effects of the addition of those elements are as follows. Addition of trace amount of the additives enables to achieve easily refined crystal grains even when solution-treating is performed at a temperature at which Ti can be sufficiently solid-soluted, and to improve spring property by virtue of hardening caused by heat treatment at a low temperature after pressing described below. Even though addition of group III elements are employed in prior art, the present invention differs from the prior art regarding the intention of the addition which is not only for precipitation hardening. Fe is the most effective additive used for the titanium-copper alloys of the present invention.

It is expected that elements such as Co, Ni, Si, Cr, V, Nb and Zr are also effective similar to in the same manner as Fe. The effect can be observed in the addition of single additive of them, while they can be added in a combination of two or more. Since each of these elements has small amount solid-soluted in a titanium-copper alloy, a very small amount of the addition enables refinement of crystal grains. These elements do not affect the development of a modulated structure that improves strength of the titanium-copper alloy. Each of B and P has little effect on the alloy with single use, but enhances the effect of the other elements when one of which is added in combination with the other elements. The above elements show effects when the total content thereof is 0.05 mass % or more. However, too much amount of the additives eventually causes a narrower region composed of solvus of Ti, resulting in tendency of precipitation of coarse second phase particles, which slightly improves strength but deteriorates bendability.

Adverse effects become prominent when the total amount of group III elements exceeds 0.5 mass %. With respect to the preferable range of the amount of these group III elements, the amount of Fe is 0.17-0.23 mass %, the amount of any one of the elements selected from Co, Ni, Cr, Si, V, Nb, Mg and Sn is 0.15-0.25 mass %, and the amount of any one of the elements selected from Zr, B and P is 0.05-0.10 mass %.

The present invention is able to provide a copper alloy excellent in both of strength and bendability by manufacturing method comprising adding proper amounts of only elements effective in refinement of crystal grains in a titanium-copper alloy and carrying out appropriate processes. The amount of group III elements to be added in the present invention is not one for precipitation hardening, but trace amount for refinement of crystal grains. Therefore, in the copper alloy of the present invention, hard precipitates promoting wear-out of stamping dies hardly precipitate, accordingly the copper alloy of the present invention are excellent in preventing the wear-out of stamping dies.

(c) C and O

As recited above, in the copper alloy of the present invention, the group III elements effectively refinement crystal grains in the course of solution treatment process in which. Ti is solid-soluted in a matrix. The each of the content of C and O is specified in the present invention for the purpose that the group III elements effectively contribute to the improvement of strength.

When an alloy contains large amounts of C and O, a portion of these group III elements exist as stable oxides and/or carbides, resulting in hindering suppression of the development of recrystallizing grain during solution treatment and in limited hardening even when adequate heat treatment is performed after press forming. Further, when group III elements become oxides and/or carbides, they fail to contribute to the improvement of strength, and become detriments to bendability in the same manner as non-metallic inclusions. It is considered that C contained in the copper alloys is derived from residual grease on the surfaces of the structural member of the apparatus with which molten metal is contacted during the ingot manufacturing process or contained in the raw material to be melted. O contained in the copper alloy is derived from oxygen in the ambient air that dissolved in the molten metal during the ingot manufacturing process.

In order to achieve high strength and excellent bendability which are objects of the present invention, it is preferable to decrease the content of O and C as much as possible, however if each of the contents of C and O can be kept at 0.010 mass % or less, the effect of C and O can be ignored.

(d) Other Impurity Elements

In the present invention, “other impurity elements” refer to elements other than Cu, Ti, Fe, Co, Ni, Si, Cr, V, Nb, Zr, B, P, C and O, exemplarily mentioned are S, Pb, Sn, and Zn that have low melting points and are easily solid-soluted in a titanium-copper alloy. The higher ordinality and homogeneity of the amplitude and wavelength in the profile of titanium density become, the more preferable a modulated structure of a titanium-copper alloy is for achieving high strength and bendability. It is considered that these other impurity elements cause disorder in the regularity and homogeneity of the modulated structure, and therefore they should be reduced as much as possible. Further, the hardening phenomenon found after heat treatment at low temperatures subsequent to cold working is observed prominently when dislocation density before heat treatment is homogeneously distributed. As may be expected, disorder in the development of the modulated structure results in a heterogeneously distributed dislocation density after cold working. Exceeding 0.050 mass % of these impurity elements adversely effect on the development of the modulated structure and unfavorable since they result in insufficient hardening even when adequate heat treatment is performed after press forming.

(3) Low-Temperature Heat Treatment after Press Forming

Ii is able to improve spring property of the alloy of this invention more, by the fundamental manufacturing processes of solution treatment, cold rolling and aging treatment in this order, pressing into a leaf spring such as connectors, and heat treatment at 400° C. or less, which is less than aging treatment temperatures. Because this heat treatment which is performed at this stage is one after forming the final product shape, it is preferable to be conducted in an inert-gas atmosphere to prevent surface oxidation. Favorable heating conditions generally fall in the range of 1 to 5 hours at 340-360° C., slightly changes depending on the type and amount of the added elements. In the present invention, with respect to “spring property”, one which is able to store more elastic energy is treated as having more spring property. In other words, the broader the elastic region is and the higher the elastic upper limit is on a load versus deflection curve, the greater spring property a spring has,

Accordingly, in general, the higher yield strength of a material provides better spring property. Also, when yield strengths are the same, a spring composed of the material having a lower Young's modulus has better spring property. In the alloy of the invention, the reason why spring property is improved by heat treatment at a low temperature after pressing is not that further development of the modulated structure, but that an effect of trace amount of additives of group III elements. This effect is firstly observed in the present invention.

Mobile dislocations occur in a bending zone soon after pressing and the existence thereof decreases the elastic limit slightly. However, it is considered that heat treatment at a low temperature thereafter firmly fixes the mobile dislocations due to the group III elements specified above, and therefore the strength is improved. That is, a maximum stress is applied to bending zone of a spring shape providing an axis when a load is applied to the spring so as to give deflection. Therefore, the reinforcement of this zone brings improved spring property.

The present invention also provides an advantage that the dimensional change of the product is small even when low-temperature heat treatment is performed after press forming for the purpose of improving spring property. The reason is that the modulated structure accompanied with a volume change never develops any more due to that the heat treatment temperature is lower than the aging temperature of titanium-copper alloy.

(4) Manufacturing Method

As recited above, the base metal is strengthened by aging treatment that brings a structure in which local density of titanium periodically changes within the matrix, i.e., by development of a modulated structure. Precipitates such as TiCu₃ that are easily formed in a titanium-copper alloy never contribute to precipitation hardening as well as often deteriorate bendability. Such detrimental precipitates are formed when the solution treatment temperature is low and/or when the aging treatment temperature is high.

In the present invention, the temperature that most effectively develops a modulated structure is in a region lower than the temperature at which second phase particles precipitates. Hence, by performing solution, treatment by which the second phase is solid-soluted, followed by aging treatment in the proper conditions, second phase particles are hardly formed. Herein, “proper aging treatment conditions” refer to the conditions in which second phase particles do not precipitate as TiCu₃ stable phase in grain boundaries, and strength of the alloy becomes maximum. Proper aging treatment conditions changes depending on the working ratio of the cold rolling performed before aging treatment and the type and amount of the group III elements to be added. Excessive aging treatment causes stable phase precipitated in grain boundaries resulting in deteriorated strength and bendability, that is “overaging”.

Further, in solution treatment before aging treatment, the higher solution treatment temperatures, the faster the ratio of solid-soluting of precipitates. It is therefore preferable to select a temperature of solution treatment as high as possible in order to perform sufficient solution treatment. The fundamental processes of the present invention include solution treatment with a temperature at which titanium is completely solid-soluted, adequate cold rolling in order to adjust the temper and to adjust the thickness of the product, and then aging treatment at a relatively low temperature to prevent the development of a stable phase. The present invention is also characterized by refinement of crystal grains by solution treatment.

In spite that Group III elements are added in order to refine recrystallizing grains, the amount of the added elements is trace, thus a solution treatment at too high temperature causes coarse grains, and the object of the present invention cannot be achieved. It is therefore preferable to reduce the role of the final solution treatment by performing sufficient solution treatment during the foregoing processes in advance. The sufficient foregoing solution treatment almost completely prevents second phase particles remained before the final solution treatment, thus in the final solution treatment, recrystallizing anneal is merely required such that new second phase particles do not precipitate.

Specifically, an alloy is heated to a temperature slightly above the solvus of an equilibrium diagram followed by quenching.

The “foregoing solution treatment” recited above refers to early stage processes of a material. Exemplarily, sufficient solution treatment is performed on a raw coil having a thickness of 5 times or more of that of the product, preferably 10 times or more. “Sufficient solution treatment” refers to performing solution treatment at a temperature that eliminates the second phase in a short period of time. However, unnecessarily high temperature is unfavorable since internal oxidation of Ti and group III elements dissolved in solid-solution occurs from the surface layer into the metal at the temperature, which oxidation is caused by oxygen that penetrates from the surface and diffuses inside of the alloy. This oxidation depends on the oxidation properties of Ti and the group III elements to be added, but the tendency of oxidation is enforced by heating to high temperatures exceeding 950° C.

Therefore, the solution treatment temperature of the process recited above is preferably in the range of 850-900° C. Performing sufficient solution treatment in the process recited above provides a single phase structure, improvement of ductility, and ease of the subsequent cold rolling.

It is preferable to perform sufficient solution treatment in the process recited above followed by cold rolling, and a final solution treatment at a temperature just above the solvus of the second phase. Practically, there is fluctuation in the processing temperature and alloy composition of the system, and therefore a miniscule amount of second phase particles (Cu—Ti—X-type) containing group III elements precipitate. In the present invention, it is preferable to exclude second phase particles. However, if second phase particles having substantially round shapes do not grow coarsely, and if they are dispersed finely and uniformly, the adverse effect thereof on strength and bendability is exceedingly small.

Therefore, it is not necessary to perform the final solution treatment in the conditions in which second phase particles are completely eliminated. Thus the final solution treatment can be performed at a preferable range from just on the solvus to about 10° C. above. On the other hand, as the solution treatment temperature is decreased, a phenomenon is observed wherein the second phase rapidly precipitates in lamellar constituent. Such structure results in significant deterioration of strength and bendability.

From the above, the fundamental processes to make an alloy of the present invention include the following:

“a sufficient solution treatment (the first solution treatment); cold rolling (an intermediate rolling); the final solution treatment (the second solution treatment) just above the solvus of components of second phase particles; cold rolling (the final rolling); and aging treatment in this order.”

Regarding the processes before the first solution treatment, a metal composition having a specified formulation is melted, and then casting and hot rolling are performed, and then, cold rolling and annealing can be appropriately repeated, conversely, the first solution treatment can be performed immediately after hot rolling.

The following is a description of processes in the order of an exemplary embodiment of the present invention.

1) Ingot Manufacturing Process

Melting and casting are fundamentally performed in a vacuum or inert gas atmosphere. An appropriate amount of Cu is melted, and one or more elements, selected from the group consisting of Fe, Co, Ni, Si, Cr, V, Nb, Zr, B and P as a group III element are added in the amount of 0.01-0.50 mass % in total. After sufficient maintaining of the composition in melting conditions, 2-4 mass % of Ti is added, and then Ti and the other added elements are completely melted, the molten metal is cast into a mold to form an ingot.

Some in the group III elements of the present invention are metals with high melting points, and therefore it is necessary to maintain the melting conditions sufficiently in order to avoid solid residue, while Ti tends to melt in Cu much easier than group III elements, and can be added after the melting of the group III elements.

The content of O and/or C is adjusted by the degree of vacuum and purity of inert gas. When the degree of vacuum and/or the purity of the inert gas are low, not only oxygen dissolves into the molten metal, but also reacts with a carbon-containing zone in the structural member of the apparatus such as crucibles and nozzles with which the molten metal contact, resulting in producing carbon dioxide gas that brings carbon into the molten metal. Industrially, use is made of scrap metal as a melting material in order to reduce raw material costs. However, residual grease contained in the scrap brings O, C and S incorporated in the alloy, thus it is necessary to wash scrap metal when it is used.

2) Subsequent Processes after Ingot Manufacturing Process

The cast ingot prepared as above is subjected to a homogenization anneal for 3 hours or more at 900° C. or more, since it is desirable to eliminate segregation completely and crystals occurred during casting at this stage. Homogenizing treatment anneal is effective for dispersing the precipitates of second phase particles finely and uniformly during solution treatment described below, and for prevention of mixed grain size. Then, hot rolling, repeated cold rolling and annealing, and then solution treatment are performed. Since low temperatures during the intermediate annealing may form second phase particles, the annealing is performed at a temperature at which the second phase particles are completely solid-soluted. With respect to normal titanium-copper alloys without including group III element additives, the annealing temperature may be 800° C. However, in the case of the titanium-copper alloy of the present invention having added group III elements, it is preferable to select a temperature of 850° C. or more.

The heating rate and cooling rate during solution treatment should be as fast as possible to prevent precipitation of second phase particles during the heating and cooling steps. Performing the final solution treatment of the alloy in a state in which the second phase is completely solid-soluted enables the added group III elements to act effectively to obtain a fine and homogenous structure. After the final solution treatment, cold rolling is performed with an adequate working ratio in order to adjust the temper, and finally aging treatment is carried out to prepare the final product. It is necessary to be careful with a stable phase, i.e., TiCu₃ not to occur during aging treatment.

3) Final Solution Treatment

During the final solution treatment of the fundamental processes of titanium-copper alloy, it is preferable that the second phase is solid-soluted completely. However, a high temperature necessary to form a solid-solution completely causes coarse crystal grains, and therefore a heating temperature should be in the vicinity of the solvus at which second phase particles are sold soluted. Rapid heating to this temperature and rapid cooling suppresses the occurrence of coarse second phase particles.

A short heating time during the final solution treatment produces fine crystal grains. At this stage, even if second phase particles occur, particles dispersed both finely and uniformly have almost no adverse effect on strength and bendability. Since coarse particles tend to develop further in the final aging treatment, and therefore any second phase particles that develop at this stage must be few and small.

4) Final Cold Rolling Working Ratio and Aging Treatment

Cold rolling and aging treatment are performed after the final solution treatment process recited above. A reduction ratio of 25% or less for cold rolling is preferable. The higher working ratios, the more second phase particles tends to precipitate in the grain boundaries in subsequent aging treatment. Lower temperatures during aging treatment more suppress the second phase particles to precipitate in the grain boundaries. Although various conditions may provide similar strengths, low temperatures for long period of time are more effective than high temperatures for short period of time in order to suppress grain boundary precipitation of second phase particles.

Within 420-450° C. which is a proper range used for aging treatment temperature in prior art, aging treatment gradually improves strength, while second phase particles tend to precipitate in grain boundaries, thus even slight overaging decreases bendability. Proper condition for aging treatment of the invention varies depending on the added elements, however it can be said that 400° C. at the highest for 12 hours, and aging treatment at low-temperature can be performed at 380° C. for longer heating time of 24 hours.

5) Press Forming and Low-Temperature Heat Treatment

The alloy of the present invention may be used as parts without any process after pressing into a desired spring shape. Also, heat treatment at a low temperature after pressing hardens the plastic-deformation zone, resulting in further improved spring property. The following formula expresses the range of the suitable heating condition to produce such hardening phenomenon.

2×3^((370-X)/10) ≦Y≦2×3^((400-X)/10)

Herein, X in degree “° C.” refers to heating temperature and Y in degree “minute” refers to heating time.

A more preferable formula is as follows.

Y(minutes)≈2×3^((380-X)/10)

EXAMPLES

Herein, non-limiting examples of the present invention are described. In manufacturing the copper alloys of Examples of the present invention, since active metal of Ti was added as a second component, melting was performed in a vacuum or in an inert gas (such as Ar). Relatively pure raw materials were carefully selected in order to prevent any undesirable adverse effects due to the inclusion of impurity elements other than the elements specified in the present invention.

Firstly, in all of Examples 1-7, Reference Examples 8-10 and Comparison Examples 11-18, any of Fe, Co, Ni, Cr, Si, V, Nb, Zr, B and P was added to Cu according to the formulations illustrated in Table 1. Then, Ti as illustrated in Table 1 was also added. The holding time after the addition of the elements was carefully examined in order to obviate undissolved residue of the added elements. After sufficient holding time, the molten metal was poured into a mold in an Ar atmosphere to manufacture ingots each having about 2 kg.

The above obtained ingots were coated with an oxidation inhibitor, dried at room temperature for 24 hours, heated at 950° C. for 12 hours, hot-rolled, and formed into plates of 10 mm thickness. The plates were again coated with an oxidation inhibitor to suppress segregation, heated at 950° C. for 2 hours, and then water-cooled. This water cooling was employed in order to preserve the solid-solution state as much as possible. In other words, a single phase structure has better ductility, thus improves ease of the subsequent cold rolling. In addition, coating with an oxidation inhibitor was employed in order to prevent oxygen penetrating from the surface and reacting with the added element components and to minimize grain boundary oxidation and internal oxidation which causes inclusions.

The hot-rolled plates were then mechanically ground and pickled to remove scale. The plates were then cold rolled to a material thickness of 1.5-2.0 mm. After the first solution treatment, the plates were cold-rolled to an intermediate thickness of 0.18-0.6 mm. Then, as the final solution treatment, the plates were placed in a rapid-heating annealing furnace and heated at 50° C. per second to the respective temperature of the solvus of the second phase particle composition (for example, 800° C. for a composition having contents of Ti of 3 mass % and Fe of 0.2 mass %). The plates were then maintained at the temperature for 2 minutes and water quenched. Finally, the plates were further pickled to remove scale, cold rolled to a thickness of 0.15 mm, and aged in an inert gas atmosphere to obtain test pieces of Examples of the present invention. The test pieces of the Comparison Examples were obtained by adjustment of composition or manufacturing processes.

TABLE 1 No Ti Fe Co Ni Cr Si V Nb Zr B P O C S Al, Ca, Pb, Sn, Zn Examples 1 3.4 0.08 — — — — — — — — — 0.002 0.003 0.003 0.003 2 2.4 0.20 — — — — — — — — — 0.001 0.001 0.002 0.004 3 2.9 0.19 — — — — — — — — 0.03 0.003 0.001 0.004 0.003 4 3.2 — — — 0.20 — — — — — — 0.002 0.002 0.003 0.002 5 3.3 — — — — — — — 0.05 0.02 — 0.001 0.002 0.002 0.004 6 3.1 0.18 — — — — — — — — — 0.002 0.001 0.001 0.003 7 3.0 — 0.01 0.01 0.15 0.01 0.01 0.01 — — — 0.002 0.002 0.003 0.005 Reference 8 3.2 — — — 0.15 — 0.15 — — — — 0.003 0.002 0.002 0.002 Examples 9 3.3 — 0.15 0.15 — — — — — — — 0.001 0.002 0.002 0.003 10 3.6 — — — — 0.27 — — — — — 0.002 0.002 0.001 0.004 Comparison 11 3.1 0.21 0.23 0.22 0.07 0.12 0.11 0.09 — — — 0.003 0.003 0.005 0.005 Examples 12 3.2 — — — — — — — 0.07 0.03 — 0.002 0.025 0.003 0.007 13 3.2 — — — — 0.31 — — — — — 0.032 0.003 0.004 0.006 14 3.1 — — — — 0.25 — — 0.06 — — 0.028 0.025 0.003 0.008 15 3.2 0.19 — — — — — — — — — 0.022 0.023 0.063 0.003 16 3.2 0.18 — — — — — — — — — 0.001 0.001 0.003 0.078 17 3.1 — 0.01 0.01 — — — — — — 0.02 0.001 0.001 0.003 0.002 18 3.2 — — — — — — — — — — 0.002 0.003 0.003 0.003 Dashes in the table represent no additives.

TABLE 2 A B C First solution First solution Final solution D E treatment treatment plate treatment Final cold rolling Aging treatment No. conditions thickness (mm) conditions reduction ratio (%) conditions Examples 1 850° C. × 10 min. 1.5 800° C. × 1 min. 18 380° C. × 24 h 2 870° C. × 10 min. 2.0 800° C. × 1 min. 25 380° C. × 24 h 3 870° C. × 10 min. 1.8 800° C. × 1 min. 20 400° C. × 12 h 4 850° C. × 10 min. 1.5 800° C. × 1 min. 20 400° C. × 12 h 5 850° C. × 10 min. 1.8 800° C. × 1 min. 20 380° C. × 24 h 6 870° C. × 10 min. 2.0 800° C. × 1 min. 20 380° C. × 24 h 7 870° C. × 10 min. 1.5 800° C. × 1 min. 20 400° C. × 12 h Reference 8 850° C. × 10 min. 1.5 800° C. × 1 min. 40 450° C. × 12 h Examples 9 850° C. × 10 min. 2.0 720° C. × 3 min. 25 380° C. × 24 h 10 820° C. × 5 min.  3.0 800° C. × 1 min. 20 380° C. × 24 h Comparison 11 870° C. × 10 min. 1.5 800° C. × 1 min. 20 400° C. × 12 h Examples 12 850° C. × 10 min. 1.8 800° C. × 1 min. 20 400° C. × 12 h 13 960° C. × 10 min. 2.0 800° C. × 1 min. 20 380° C. × 24 h 14 850° C. × 10 min. 1.5 800° C. × 1 min. 20 400° C. × 12 h 15 870° C. × 10 min. 2.0 800° C. × 1 min. 25 380° C. × 24 h 16 870° C. × 8 min.  1.8 800° C. × 1 min. 20 400° C. × 12 h 17 860° C. × 10 min. 2.0 800° C. × 1 min. 25 380° C. × 24 h 18 860° C. × 8 min.  1.8 800° C. × 1 min. 20 400° C. × 12 h

A tensile test was performed, in which 0.2% offset yield strength was measured. A W bend test was performed wherein a minimum bending radius at which cracks do not occur was defined as the minimum bend radius (MBR), and the ratio of the MBR to the thickness (t), i.e., the MBR/t ratio, was evaluated.

Then, spring property was evaluated by performing two types of load tests based on common connector shapes. In one type of the load test, a load was applied such that the bending zone contracts in the direction of the bending, and in the other type of the load test, a load was applied in the opposite direction such that the bending zone expands. For convenience, the evaluations are herein referred to as Evaluation 1 (former one) and Evaluation 2 (latter one). Evaluations 1 and 2 are described below.

Evaluation 1:

Evaluation 1 is directed to evaluate the spring property of a bellows type connector as illustrated in FIG. 1. FIG. 2 illustrates the shape of a test piece. The test piece has a pin width of 1.6 mm, a bending zone angle of 45 degrees, a bending zone curvature radius of 0.7 mm, and a 4 mm arm length, i.e., a 4 mm straight-line length from the bending zone to the point of force. As illustrated in FIG. 3, a test piece (spring) is fixed by a plate holder, a piston head connected to a load cell displaces the spring, and the applied load is measured, thereby the relationship between load and deflection is shown.

The cross head speed during Evaluation 1 is 5 mm per minute. The position where the loaded point contacts with the test piece is referred to as “initial position a.” The test piece is pressed and displaced 2 mm vertically to a position referred to as “turn-back position b,” where the test piece is held statically for 5 seconds. Then, the piston head returns to the stand-by position at a speed of 5 mm per minute. Then the point on the test piece that contacts with the piston head, elastically returns to a position referred to as a′. When the test piece is plastically deformed, that point does not return to the initial position. The difference expressed by c=a−a′ is defined as “permanent deflection c.”

The load imposed on the piston head at the turn-back position is defined as “maximum load Pmax.” The load-deflection curves produced by this evaluation are shown in FIG. 4. During this evaluation cycle, the piston head is coated with lubrication oil in order to minimize frictional resistance arose from the test piece. In this Evaluation, the test piece having a high maximum load “Pmax” and a small permanent deflection “c” is considered to have high spring property.

To investigate the effect of hardening by low-temperature heat treatment, a test piece is pressed to form a shape illustrated in FIG. 1, then heat treatment is performed on the test piece in an Ar gas atmosphere at 350° C. for 1 hour and the maximum load and permanent deflection were measured. The maximum load after heat treatment is referred to as Pmax*, and the permanent deflection after heat treatment is referred to as c*. Table 3 illustrates c (mm), c* (mm), and Pmax (N) and Pmax* (N) respectively.

Evaluation 2:

As illustrated in FIG. 5, Evaluation 2 is directed to evaluate the spring property of a press-formed connector in which force is applied so as to expand the bending zone when connectors are fit together by insertion. FIG. 6 illustrates the test piece shape. The test piece is formed by pressing in a compression test machine using a jig for the W bend test specified in JIS H 3110.

In fabricating test pieces, it is considered that a large curvature radius of a bending zone is preferable in order to reduce the influence of surface roughness or other anomalies of the bending zone, and therefore pressing was performed using a jig having a bending zone curvature radius of 1.5 mm. FIG. 7 illustrates the testing method. Test piece immediately after press forming is placed with the bent elbow pointing upward, and the height to the top of the bending zone is defined as “initial height d.”

The test piece are placed in a die and squeezed such that the elbow shape is press formed and displaced downward. A die of high rigidity is used in order to avoid deformation of the die. In this evaluation, a spacer of 2 mm thickness is used such that the test piece is fixed with a distance between the upper die and lower die of 2 mm, then the test piece is maintained at this state for 24 hours. After removing the load, the height to the bending zone is again measured, and this height is defined as “f”. The height variation of the test piece is defined as “g” which is the difference between d and f. A small g indicates that the restoring force is high after being loaded for an extended period of time, and therefore spring property is high. Similar evaluation is performed for the test piece prepared by heat treatment at 350° C. for 1 hour subsequent to press forming. Thus, the height variation of the test piece was determined, and this result is referred to as g*. Table 3 illustrates g (mm) and g* (mm).

TABLE 3 No. YS (MPa) MBR/t c (mm) Pmax (N) c* (mm) Pmax* (N) g (mm) g* (mm) Examples 1 861 1.5 0.365 3.07 0.133 3.15 0.392 0.083 2 852 0.5 0.372 3.03 0.140 3.05 0.398 0.088 3 887 1.0 0.356 3.13 0.125 3.25 0.383 0.076 4 915 1.0 0.335 3.28 0.108 3.42 0.365 0.057 5 924 2.0 0.328 3.30 0.102 3.50 0.352 0.050 6 906 1.0 0.338 3.25 0.113 3.38 0.377 0.064 7 917 1.0 0.333 3.27 0.107 3.43 0.363 0.057 Reference 8 735 4.5 0.537 2.62 0.526 2.61 0.492 0.427 Examples 9 723 4.5 0.553 2.67 0.558 2.65 0.498 0.432 10 802 4.0 0.430 2.83 0.410 2.95 0.547 0.456 Comparison 11 935 6.0 0.320 3.35 0.103 3.52 0.345 0.052 Examples 12 823 1.0 0.353 2.92 0.342 2.91 0.387 0.230 13 816 4.0 0.350 2.88 0.335 2.87 0.388 0.243 14 922 5.0 0.329 3.32 0.318 3.30 0.358 0.210 15 873 1.5 0.353 3.10 0.323 3.12 0.386 0.183 16 867 1.5 0.358 3.09 0.325 3.10 0.389 0.188 17 765 3.5 0.487 2.77 0.462 2.78 0.451 0.315 18 753 3.0 0.483 2.75 0.460 2.74 0.467 0.323

Table 3 illustrates that the test pieces of Examples all have 0.2% offset yield strengths of 850 MPa or more and MBR/t ratios of 2.0 or less, and thus they exhibit both high strength and excellent bendability. Further, in the evaluations of spring property, all of them showed permanent deflection of 0.40 mm or less and maximum loads of 3.0 N or more in Evaluation 1, and height variations of 0.40 mm or less in Evaluation 2 which represents excellent spring property.

The spring property was further improved by heat treatment at 350° C. for 1 hour subsequent to press forming of a test piece.

On the other hand, in Reference Example 8, the strength and bendability decreased due to a precipitation of a stable phase in grain boundaries caused by a high reduction ratio in the final rolling and a high temperature in aging treatment. In Reference Example 9, strength and bendability decreased due to a precipitation of second phase in lamellar constituent because the temperature of the final solution treatment was low even though the metal contains Ti, Co and Ni, prohibiting solid-solution of Ti, Co and Ni. In Reference Example 10, the strength and bendability decreased because the second phase failed to be solid-soluted in the final solution treatment due to an insufficient solution treatment in the foregoing processes.

In Comparison Example 11, bendability was poor because second phase particles precipitate excessively due to the amount of group III elements of more than 0.5 mass % in total. In Comparison Example 12, C was contained in an amount of more than that of the present invention, therefore Zr reacted with the excess carbon to generate carbide compound which precipitated in the alloy. The precipitates hardly contributed to improvement of the strength of the material, and even when adequate heat treatment was performed after press forming, spring property was not improved.

In Comparison Example 13, strength and bendability decreased because internal oxidation occurred due to the temperature in the solution treatment of the foregoing processes higher than that required. Therefore, even when suitable heat treatment was performed after pressing, spring property improvement is hardly observed. In Comparison Example 14, the amounts of C and O were higher than the amounts defined in the present invention because melting was performed in a melting furnace with a low vacuum degree, and charcoal was used to cover the molten metal. As a result, Si and Zr existed as oxide and/or carbide inclusions, which did not enhance strength, decreases bendability, and even when heat treatment was performed after pressing, spring property was not improved. In Comparison Example 15, scrap metal was used as the material to be melted. The contents of C and S were high because the scrap metal was melted without removing pressing oil and milling oil therefrom and without desulferization. Therefore, even when heat treatment was performed after pressing, the spring property was not improved. In Comparison Example 16, scrap metal was used as the material to be melted in which impurities such as Al, Ca, Pb, Sn and Zn were contained. Therefore, even when heat treatment was performed after press forming, the spring property was not improved. In Comparison Example 17, strength and bendability were inferior because the amounts of Co, Ni and P added as group III elements were not sufficient for the amounts specified in the invention. Therefore, even when heat treatment was performed after press forming, spring property hardly showed improvement. In Comparison Example 18, strength and bendability were inferior because none of the group III elements specified in the invention was added. Therefore, even when heat treatment was performed after press forming, the spring property showed no improvement. 

1. A copper alloy for electronic components comprising 2.0-4.0 mass % of Ti, 0.05-0.50 mass % in total of one or more elements selected from the group consisting of Fe, Co, Ni, Si, Cr, V, Nb, Zr, B and P, and the balance being Cu and other impurity elements, wherein the total amount of other impurity elements is 0.050 mass % or less; and the contents of each C and O are 0.010 mass % or less.
 2. A copper alloy for electronic components comprising 2.0-4.0 mass % of Ti, 0.05-0.50 mass % of Fe, and the balance being Cu and other impurity elements, wherein the total amount of other impurity elements is 0.050 mass % or less; and the contents of each C and O are 0.010 mass % or less.
 3. The electronic component prepared from the copper alloy of claim 1 or 2 wherein the hardness is adjusted by heat treatment at a temperature of 400° C. or less after pressing of the copper alloy into a predetermined shape. 